Really good write up Sid. I have always been suspicios that VinylEster may not be 100% Ethanol proof. There are also Ethanol resistant sloshing compounds, but while they are resistant, they are not Ethanol Proof. Seems to me there was a post a couple of years ago on here about a highly recommended Ethanol "proof" slosh compound.
FWIW, I built my tanks with SafetyPoxy some 16 years ago and they have been in service for 15 years and some 900 flight hours. I also sloshed them with what would now be considered to be a lower grade alcohol resistant sloshing compound. I did run some alcohol through the tanks back when the plane was new, but haven't had any in the tanks in 15 years now. Since then, it has had a steady diet of 100LL with the exception of one tank full of 80/87 red gas I was able to buy about 10 years ago. After 15 years, the tanks and sloshing compound all appear to be in excellent condition with no slosh or tank residue in the sumps. But, I very specifically avoid mogas so as to avoid any chance of alcohol contamination. Those with Aluminum tanks probably have a much better tolerance for alcohol contamination. A couple of years ago I rebuilt the tip tanks off from a Cherokee 235. Those tanks were built with polyester resin. Teh owner of the plane swore that he always tested his fuel for alcohol and had never observed any alcohol in the fuel he had put in the plane. The tip tanks had become so soft that they were deforming in flight. When I cut them open, I found the inner layer of the tanks to be pretty much melted away with pockets of gas held within the glass all over the tanks. I ground out the pockets as best I could and literally built a new tank within the old tank shells so they would hold fuel. However, with the amount of fuel saturation in the outer shell of the tanks, he found that they simply could not be cleaned up well enough to hold paint. For all practical purposes, he really should have replaced the tanks with new, which was a 6 month lead time and $6000 for two tip tanks. -Jeff Scott Los Alamos, NM ----- Original Message ----- From: Sid Wood Sent: 07/12/12 08:52 AM To: kr...@mylist.net Subject: KR> Ethanol Compatibility I remember Mark Langford saying that public confessions were good for the soul or something like that. That also makes it more difficult to get elected to political office. I am looking for neither of those concerns. I once recommended building fiber glass fuel tanks using Vinyl Ester Resin. All sources that I could find did say that Vinyl Ester was compatible with the Ethanol found in most automobile fuels today. Conversely, Epoxy was not compatible with Ethanol. I built the wing tanks in my Diehl wing skins using Vinyl Ester Resin per the Diehl instructions. When I put in 92-octane auto fuel containing 10 percent Ethanol, I got the same reaction as if the tanks were made with Epoxy. Surfaces slowly started to dissolve, fuel turned yellowish brown and a sticky brown goo starting clogging the sumps. I researched my sources on the internet and all still confirmed my previous conclusion. Looking a little further on solvency chemistry, I found internet sites that address ways to enhance solvent action. Pure Ethanol, gasoline and water are excellent solvents by themselves, but none of these alone will effect cured Vinyl Ester. Adding 6 percent water to Ethanol will produce a solvent that will slowly dissolve Vinyl Ester. So, how much water would that actually be in auto fuel containing 10 percent Ethanol? The math is easy: 10 percent of 6 percent is 0.6 percent. That's less than 1 ounce per gallon. Where does the water come from? From the moisture in the air, the Ethanol will readily adsorb the water in half full tanks, especially if there is a vent like most aircraft tanks (like mine). I now have drained the tanks and left the caps off. After 2 weeks the goo on the inside surfaces has "re-cured" hard just like the original. The quick-drains had become clogged and have been replaced. One concern is the integrity of the tank walls; there is an imprint of the foam layer sandwiched between the inner and outer wing surface, top and bottom, that outlines the wing tanks. This imprint pattern appeared when the drying out process was started. Any ideas what is going on with that? Long term plan now is to use 100LL. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA smw...@md.metrocast.net _______________________________________ Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. To UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html
